Aqueous dispersions of hydrophobic material are well-known and used in numerous applications. For instance, in papermaking, aqueous dispersions of hydrophobic material are used as sizing agents in order to give paper and paper board some degree of resistance to wetting and penetration by aqueous liquids. Examples of hydrophobic materials widely used for sizing include cellulose-reactive sizing agents, e.g. alkyl ketene dimers and substituted succinic anhydrides, and non-cellulose-reactive sizing agents, e.g. rosin-based and resin-based sizing agents.
Dispersions of hydrophobic material generally contain an aqueous phase and finely divided particles or droplets of the hydrophobic material dispersed therein. The dispersions are usually prepared by homogenizing the hydrophobic, water insoluble material in an aqueous phase in the presence of a dispersant using high shear forces and fairly high temperatures. Dispersants conventionally used include anionic, amphoteric and cationic high molecular weight polymers, e.g. rignosulfonates, starches, polyamines, polyamideamines, and vinyl addition polymers. The polymers can be used singly, together or in combination with other compounds to form a dispersant system. Depending on the overall charge of the components of the dispersant system, the size dispersions will be anionic or cationic in nature.
Dispersions of hydrophobic material usually exhibit rather poor stability and high viscosity, even at relatively low solids contents, which evidently lead to difficulties in handling the dispersions, for example on storage and in use. A further drawback is that the products have to be supplied as low concentration dispersions which further increases the costs of transportation of the active hydrophobic material.
It is accordingly an object of this invention to provide aqueous dispersions of hydrophobic material with improved stability and viscosity properties. It is another object of this invention to provide improved aqueous dispersions of sizing agent, notably cellulose-reactive sizing agents. Further objects will appear hereinafter.